The carbon monoxide pockets in the hull were likely to be a result of the fire, he said.

Firefighters were still checking hot spots and had put in fans to dissipate the gas so crew could continue unloading the fish, but it was evident specialised equipment was needed that the Fire Service could not supply, he said.

The Nelson-based vessel was 85 kilometres northeast of the Lyttelton Heads when a blaze broke out in the fishmeal hold about 5.20am yesterday.

It was towed still burning into Lyttelton by the San Discovery at 12.30am today and about 22 firefighters fought the blaze until 5am.

The crew hospitalised today were not believed to have been on the ship at the time of the blaze.